Method and structure to enhance gate induced strain effect in multigate device

ABSTRACT

A FinFet formed by depositing a thin layer of polycrystalline silicon followed by depositing a stress containing material, including a high Ge percentage silicon germanium film and/or a high stress W film on top of a polycrystalline silicon film. Freeing space between fins allows stressor films to be deposited closer to the transistor channel, improving the proximity of the stress containing material to the transistor channel and enhancing the stress coupling efficiency by defining a ratio between stress level in the stressor film and stress transferred to the channel for a mobility enhancement. The stress level is enhanced by patterning by removing the n-type workfunction metal from the p-FinFET. After stripping off the soft or hard mask, the p-type workfunction metal is deposited in the n- and p-FinFET regions. The freed space specifically for p-FinFet between the fins achieves an even higher stressor coupling to further boost the carrier mobility.

FIELD OF THE INVENTION

The present invention relates to the fabrication of semiconductordevices, and more particularly, to the formation of a gate stack of ann-type FET and a p-type FET to enhance the strain level in the channelto generate carrier mobility and drive current performance benefits inmultigates or trigates.

BACKGROUND AND RELATED ART

Current techniques of forming gate stack in the FinFET device structurestarts with depositing high-k metal dielectric material such as HfO₂,Al₂O₃, or La₂O₃ by ALD process. The process can be done either followingthe fin formation, referenced as the “gate first” scheme (alsoreferenced as the metal inserted polysilicon), or it can be done afterthe formation of the source and drain in a process referred to as “gatelast”, (also referenced as “replacement metal gate” (RMG) scheme). Thegate first and gate last refer to whether a metal electrode is depositedbefore or after the high temperature activation anneals of the flow. Itis then followed by a workfunction metal deposition to set thetransistor threshold voltage. Typical materials that are employedinclude TiN, TiC, or TiAl.

Since the requirement for a threshold voltage between an n-type MOSFETtransistor and p-type MOSFET differs, the gate stack formation caninvolve a certain patterning process, e.g., to deposit either one typeof workfunction metal first on both n-type and p-type FETs, followed byremoving it from one side, and then depositing the desired workfunctionmetal to set the right threshold voltage for both types of transistors.The next step consists in depositing the gate contact material to lowerthe gate resistance. In the gate first scheme, the process is followedby an offset space deposition, and an epitaxial process to form thesource and drain of the transistors. While in the gate last (RMG)scheme, the process is followed by the middle-of-the-line (MOL)source/drain contact formation such as by a contact etch, TiN barrierlayer and W film deposition.

As the device continues to the nanometer scaling, the requirement forthe transistor drive current performance becomes increasingly moredifficult to meet. One difficulty that encountered resides in theconventional stress effect, such as an embedded silicon germanium,embedded silicon carbon source drain, and dual stress silicon nitrideliner set to boost the carrier mobility that diminishes significantlywith the scaling of the gate contact pitch.

The process typically starts with the recess of a silicon source and thedrain region, followed by a SiGe or SiC film epitaxial growth in thetrench region. Typically, it consists of three different layers, thefirst layer referenced as the buffer layer which is usually lightlydoped to provide the junction gradient control and device short channelelectrostatic benefit. Then, the process continues with the main layerheavily doped to lower the source and drain sheet resistance. A typicaldopant is boron for a p-type MOSFET, and phosphorus or arsenic for then-type transistor. The incorporation of the germanium for a p-typeMOSFET and carbon for the n-type MOSFET is by introducing the strainfrom the source and drain region to the channel region. The fact thatgermanium atom has a larger lattice constant than silicon atom producesa tensile strain in the SiGe film itself when it creates bonding withthe silicon atom. The stress is then transferred to the channel regionto generate a compressive strain that is favorable for the transport ofholes and thus enhances the p-type MOSFET drive current. The effect ofthe carbon atom is just the opposite. The fact that carbon atom has asmaller lattice constant than silicon atom produces a compressive strainin the SiC film itself when it creates bonding with the silicon atom.The stress is then transferred to the channel region to generate thetensile strain that is favorable for the transport of electrons and thusenhances the n-type MOSFET drive current. The stress effect from theembedded source drain either is made of SiGe or SiC that dropssignificantly when the device gate pitch continues to scale. The pitchscaling is necessary because of the chip area reduction set to improvethe cost structure of the semiconductor. However, because of the pitchscaling, the available space for the source and drain stressor formationbecoming smaller and smaller, this leading to the decrease of thestressor volume and a greatly reduction of the stress effect from thesource and the drain region. The stress effect has been estimated to beabout only 20-30% left when the technology feature size shrinks from the22 nm node technology to the 14 nm node technology.

Another factor that limits the usage of source and drain extrinsicstressor is the transition from the planar device structure to theFinFFT type of the transistor structure. The fact that FinFET device isprovided of a thin slab of silicon as the channel (typical dimensionsare 10 nm width and 30 nm tall) which signifies that the area for stresscoupling is much reduced compared to the planar device structure whichmakes the stress coupling efficiency, defined as the ratio betweenstress level in the source and drain region to the stress level in thedevice channel region that becomes significantly less compared to theplanar device. The reduction of the aforementioned two effects (stressorvolume and stress coupling) makes the stress engineering of the FinFETdevice structure ever more challenging compared to that of previousgenerations.

The challenge for the gate induced strain, however, is how to implementit through the selection of gate stack materials to meet not only thechannel strain requirement for carrier mobility boost, but also aworkfunction setting to meet the transistor threshold voltagerequirement. It further has to have minimized gate stack inversionthickness impact so that the transistor drive current benefit from gateinduced strain will not be compromised. Gate stack materials such asTiN, TaN, and TiC have a certain level of strain itself, preferably inthe range of 2 GPa to 3 GPa which is quite significant in terms ofproducing channel strain when the coupling ratio is sufficiently high.The contact material such as W is also known for having a tensile strainfavorable for the transistor mobility enhancement.

The challenge is, as previously mentioned, how to design the gate stackthickness and structure such that the stress benefit can be maximized,but at the same time, without affecting other device parametrics, suchas the transistor threshold voltage and the inversion gate stackthickness.

SUMMARY

In one aspect, embodiments of the invention provide a method and aFinFET device structure that form a gate stack stress of a finFET toincrease the mobility and drive current.

In an embodiment, a method is described of forming a FinFET thatincludes depositing high-k dielectric on a patterned fin structure withrecess shallow trench isolation. A workfunction metal and a very thinlayer of poly crystalline silicon are then deposited on top of thehigh-k materials. A stress containing material such as high Gepercentage silicon germanium film and/or highly stress W film is thendeposited on top of the poly crystalline silicon film. In the case of ahigh Ge percentage silicon film, the film can be formed either in-situor ex-situ doped with dopant to lower the gate resistance. The in-situdoped film can be achieved by incorporating dopants during the silicongermanium epitaxial growth, whereas the ex-situ doped film can beachieved by ion-implantation following a silicon germanium epitaxialgrowth. Preferably, the gate stack has thick poly-crystalline silicon ontop of the workfunction metal that occupies the space between the fins,leaving no room for strain producing material to impart a stress in thetransistor channel for mobility enhancement.

In an embodiment, a method and structure are described freeing up thespace between the fins to allow the stressor films being depositedcloser to the channel, thus improving the proximity of the stresscontaining material to the transistor channel, thereby enhancing thestress coupling efficiency defined as the ratio between the stress levelin the stressor film and the stress transferred to the channel formobility enhancement.

In an embodiment, a method is described forming a semiconductor devicethat includes depositing high-k dielectric on the patterned finstructure with recess shallow trench isolation. A workfunction metal forn-type MOSFET is deposited on top of high-k materials. Next, apatterning process can remove the n-type workfunction metal from thep-type MOSFET. After stripping off the soft or the hard mask, a p-typeworkfunction metal is deposited in both the n-type and p-type MOSFETregions. The stress containing material can be a high percentage Gesilicon germanium film and/or a highly stress W film is then depositedon top of the poly-crystalline silicon film.

In an embodiment, the structure is provided with fins on a substrate andincludes workfunction metal and a highly stressed Tungsten (W), whereinthe workfunction metal and the highly stressed W create a strain in thechannel, with the workfunction metal wrapping around the fins. Notably,a highly stress W would fail to achieve the same results.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages describedherein will be apparent from the following more particular descriptionsof example embodiments as illustrated in the accompanying drawingswherein like reference numbers generally represent like parts ofexemplary embodiments.

FIG. 1 is a cross-sectional view of a semiconductor device having asubstrate and fin structures formed thereon;

FIG. 2 shows a cross-sectional view of a semiconductor device having asubstrate and fin structures formed thereon, with a shallow trenchisolation oxide deposited between the fins;

FIG. 3 is a cross-sectional view of a semiconductor device structure ona substrate where fin structures are formed with a shallow trenchisolation oxide recessed between the fins;

FIG. 4 illustrates a cross-sectional view of a semiconductor devicehaving a substrate and fin structures formed and covered with a high-kdielectric;

FIG. 5 is a cross-sectional view of a semiconductor device having asubstrate and fin structures formed and covered with high-k dielectricand a workfunction metal;

FIG. 6 shows a cross-sectional view of a semiconductor device having asubstrate and fin structures formed and covered with high-k dielectric,a workfunction metal, to which is added a very thin layer ofpoly-crystalline silicon film, according to an embodiment of theinvention;

FIG. 7 is a cross-sectional view of a semiconductor device having asubstrate and a plurality of fin structures formed and covered with ahigh-k dielectric, a workfunction metal, a very thin layer ofpoly-crystalline silicon film, and a high Ge percentage silicongermanium film or highly stress W film, according to one embodiment ofthe invention;

FIG. 8 illustrates a cross-sectional view of a semiconductor devicestructure having a substrate and fin structures formed with shallowtrench isolation oxide recessed in between the fins;

FIG. 9 shows another cross-sectional view of a semiconductor devicehaving a substrate and fin structures formed and covered with high-kdielectric;

FIG. 10 is a cross-sectional view of a semiconductor device having asubstrate and fin structures formed and covered with high-k dielectricand n-type MOSFET workfunction;

FIG. 11 depicts a cross-sectional view of a semiconductor device havinga substrate and fin structures formed and covered with high-k dielectricand an n-type MOSFET workfunction, with an n-type MOSFET region beingcovered by soft or hardmask for pattering, according to an embodiment ofthe invention;

FIG. 12 shows a cross-sectional view of a semiconductor device having asubstrate and fin structures formed and covered with high-k dielectricwith n-type MOSFET workfunction etched away in the p-type MOSFET regionaccording to another embodiment of the invention;

FIG. 13 is a cross-sectional view of a semiconductor device having asubstrate and fin structures formed thereon and covered with a high-kdielectric, an n-type MOSFET workfunction and p-type MOSFET according toa further embodiment of the invention;

FIG. 14 illustrates a cross-sectional view of a semiconductor devicehaving a substrate and fin structures formed thereon covered with high-kdielectric, n-type MOSFET workfunction, p-type MOSFET and a high Gepercentage silicon germanium film or a highly stress Tungsten film,according to still another embodiment of the invention; and

FIG. 15 depicts a cross-sectional view of multiple layers of gate stackin both, an n-type and a p-type MOSFET region to explain the structureprovided with a potential mobility boost from the gate stack.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,elements shown in the drawings are not necessarily drawn to scale. Forexample, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. As previously stated, thepresent disclosure relates to a semiconductor structure includinglocally thinned semiconductor fins, and a method for manufacturing thesame. Aspects of the present disclosure will now be described in detailwith accompanying figures. It is noted that like reference numeralsrefer to like elements across different embodiments. As used herein,ordinals such as “first” and “second” are employed merely to distinguishsimilar elements, and different ordinals may be employed to designate asame element in the specification and/or claims.

In a first exemplary semiconductor structure according to a firstembodiment of the present disclosure can be formed by providing asemiconductor substrate, which can be a bulk semiconductor substrate ora semiconductor-on-insulator (SOI) substrate. At least an upper portionof the semiconductor substrate includes a semiconductor material, whichcan be selected from elemental semiconductor materials (e.g., silicon,germanium, carbon, or alloys thereof), III-V semiconductor materials, orII-VI semiconductor materials. In one embodiment, the semiconductorsubstrate can include a single crystalline semiconductor material.

Generally, an upper portion of the semiconductor substrate can bepatterned by a combination of lithographic methods and an anisotropicetch used to form a plurality of semiconductor fins. The plurality offins can include two outermost semiconductor fins and at least onenested semiconductor fin located between the two outermost semiconductorfins.

As used herein, the semiconductor fin refers to a semiconductor materialportion having a pair of parallel vertical sidewalls laterally spaced bya uniform dimension. In one embodiment, each semiconductor fin can havea rectangular horizontal cross-sectional area such that the spacingbetween the pair of parallel vertical sidewalls is the same as thelength of the shorter sides of the shape of the rectangular horizontalcross-sectional area. As used herein, a fin field effect transistor(finFet) refers to a field effect transistor in which at least a channelregion is located within a semiconductor fin. As used herein, an“outermost semiconductor fin” refers to a semiconductor fin within aplurality of semiconductor fins located at an outermost location.Furthermore, a “nested semiconductor fin” refers to a semiconductor finwithin a plurality of semiconductor fins located between the twooutermost semiconductor fins of the plurality of semiconductor fins.

By way of example, a photoresist layer (not shown) can be applied overthe top surface of the semiconductor substrate and lithographicallypatterned to mask portions of the semiconductor substrate, in which aplurality of semiconductor fins is subsequently formed. The pattern inthe photoresist layer can be transferred to an upper portion of thesemiconductor substrate to form the plurality of semiconductor fins. Ifthe semiconductor substrate is a bulk substrate, the remaining portionof the semiconductor substrate underlying the plurality of semiconductorfins is referred to as a semiconductor material layer. In this case, thesemiconductor material layer is a substrate on which the semiconductorfins are formed. The semiconductor material layer functions as asubstrate mechanically supporting the plurality of semiconductor fins.The plurality of semiconductor fins and the semiconductor material layercollectively constitute a contiguous semiconductor material portion. Inone embodiment, the entirety of the contiguous semiconductor materialportion can be single crystalline. Alternatively, if the semiconductorsubstrate is a semiconductor-on-insulator (SOI) substrate, a verticalstack of a buried insulator layer and a handle substrate layer can bepresent underneath the plurality of semiconductor fins in lieu of thesemiconductor material layer. In this case, the vertical stack of theburied insulator layer and the handle substrate layer is the substrateon which the semiconductor fins are formed.

The height of the semiconductor fins can range from 5 nm to 1,000 nm,although lesser and greater heights can also be employed. The pluralityof semiconductor fins and the semiconductor material layer can be dopedwith electrical dopants, i.e., p-type dopants or n-type dopants, or beintrinsic.

Referring now to FIG. 1, a fin formation, preferably on a bulk substrate(106) is illustrated. The substrate material can be either silicon,silicon germanium, or III-V materials such as InGaAs, InAs or GaN. Thefin is preferably formed by a sidewall image transfer (SIT) process toproduce small dimensional features beyond the capability of the currentlithography tools. The silicon substrate is first deposited with theamorphous silicon, then patterned to form mandrels. Next, the SIT spaceris formed by first depositing either a silicon oxide (Si₂) or siliconnitride Si₃N₄ layer, followed by etching the SIT spacer, leavingmaterial only on the side of the mandrels. The mandrels are then pulledaway by wet etch process, leaving the SIT spacer standing alone on topof the silicon substrate, serving as a hardmask (102). A silicon finetch process is then performed to fabricate silicon fins with thedimension of 10 nm wide and 30 nm deep (104).

FIG. 2 illustrates a shallow trench isolation material (STI) deposition(108) that can be formed among the plurality of semiconductor fins. Theshallow trench isolation layer includes a dielectric material such assilicon oxide or silicon nitride or a combination thereof, referenced asa hybrid STI with good conformality and gap fill capability to fill thespace between the fins. The shallow trench isolation layer can be formedby depositing a dielectric material over the semiconductor fins and thesemiconductor material layer. The deposition of the dielectric materialcan be performed, for example, by chemical vapor deposition (CVD) orspin coating. Excess portions of the deposited dielectric material canbe removed from above the top surfaces of the semiconductor in, e.g., byplanarization preferably employing a chemical mechanical planarization(CMP). The shallow trench isolation layer laterally surrounds theplurality of semiconductor fins. The top surface of the shallow trenchisolation layer can be coplanar with the top surfaces of the pluralityof semiconductor fins. The material lying above the fin cap (102) isthen polished, as previously described.

Referring to FIG. 3, an STI etch back follows. The etching process canbe achieved by a dry etch process with chemistry to etch away either thesilicon oxide or the silicon nitride or a combination thereof (i.e.,hybrid STI). The target etch depth is 30 nm, so that the same number fin(104) is exposed above the remaining STI (108).

FIG. 4 shows a high-k material deposition (110). The material serves asthe gate dielectric to provide a high-k value to achieve a better devicedrive current benefit, but without increasing the physical thicknesswhich is prone to cause additional leakage current. Typical high-kmaterials include HfO2, Al2O3, and La2O3. The process is followed byperforming a post-deposition anneal at 700° C. in a furnace to densifythe film following the deposition. Usually because of the oxygen effect,there is a 1 nm interfacial SiOx layer formed between the high-kmaterial and the silicon substrate. The deposition is achieved by anatomic layer deposition (ALD) to achieve the thickness control and goodconformality from the top of the fin to the bottom.

FIG. 5 is an illustration of the deposition of the workfunction metal(112). A typical workfunction metal can consists of TiN, TaN, TiAlN, andTiC. The deposition is preferably achieved by the atomic layerdeposition (ALD) to obtain thickness control and good conformality fromthe top of the fin to the bottom. The purpose of the workfunction metalis to provide the right threshold voltage of the transistor so that thedevice can produce enough drive current for switching the circuit.

FIG. 6 is an illustration of the deposition of a very thin layer ofpolycrystalline silicon (114) with dimensions preferably ranging between5-10 nm. It is deposited first in the furnace as amorphous silicon, andthen annealed at a 1025° C. spike temperature to form the crystallinestructure. The purpose of the thin polycrystalline silicon layer is toprovide a template of silicon atoms to facilitate the ensuing silicongermanium epitaxial process.

FIG. 7 is an illustration of an epitaxial growth of silicon germaniumfilm (116) atop of the polycrystalline silicon. The epitaxial processcan be preferably achieved in an epitaxial chamber, starting with apre-clean by HF or pre-bake to ensure an oxide free surface, followed bysilane and other ambient with carrier gas to grow the high Geconcentration silicon germanium films. The Ge percentage canadvantageously rise to 52%. The purpose of using SiGe as the gatecontact material is because the Ge has a larger lattice constantcompared to silicon, indicative of the SiGe film having a tensile strainin the film itself. Simulation results shows that with 35% Ge silicongermanium film, the intrinsic stress level is 2 GPa. Stress can beinduced to the channel to achieve 500 MPa along the fin length and a finheight direction and 400 MPa compressive stress along the fin widthdirection. When placed atop and on the sidewall of the fin channel, itproduces strain in the channel region which is favorable for the n-typeMOSFET electron carrier transport. The SiGe film also needs to beheavily doped with either boron or phosphorous up to 5e20/cm3 to ensurethat the gate resistance is not an issue during the logic circuit or RFmicrowave transistor operation.

FIG. 8 illustrates an embodiment (200) starting from the STI etch backprocess. The etching can be achieved by a dry etch process withchemistry etching away either the silicon oxide or silicon nitride orthe combination thereof (i.e., a hybrid STI scheme). The target etchdepth can be 30 nm, such that the same number of fins (204) is exposedabove the remaining STI (208).

FIG. 9 illustrates the high-k material deposition (210). The materialserves as the gate dielectric to provide a higher-K value for betterdevice drive current benefit but without increasing the physicalthickness that may cause additional leakage current. The typical high-kmaterial used can include HfO2, Al2O3, and La2O3. The process proceedspreferably with a post-deposition anneal at 700° C. in the furnace todensify the film after deposition. Usually, because of the oxygeneffect, there is a 1 nm interfacial SiOx layer formed between the high-kmaterial and the silicon substrate. Deposition is achieved by the atomiclayer deposition (ALD) to achieve thickness control and goodconformality from the top of the fin to the bottom.

FIG. 10 illustrates the deposition of workfunction metal (212). Atypical workfunction metal includes TiN, TaN, TiAlN, and TiC. Thedeposition is achieved by an atomic layer deposition (ALD) to achievethickness control and good conformality from the top of the fin to itsbottom. The purpose of the workfunction metal is to provide a rightthreshold voltage of the transistor to ensure that the device canproduce enough drive current for switching the circuit.

FIG. 11 is an illustration of the gate stack patterning process. Thestructure is first covered with either a soft or a hard mask (216). Itthen proceeds going through a photo-lithography process to initiate thepatterning so that the n-FET region is covered while the p-FET regionopens up.

FIG. 12 is an illustration of the etch of n-type MOSFET workfunctionmetal (212) from the p-type MOSFET region. Most of the workfunctionmetal shows a certain level of strain but only favorable for one type oftransistor carrier transport. By way of example, a TaN film has atensile strain up to 2 GPa which is beneficial to the electron transportbut is detrimental to the hole transport. Furthermore, experimentally,from several dark field holography strain measurement results, one canobserve the TiN, either by ALD (25A) or PVD (140A) that induces asignificant strain in the silicon channel. The ‘Fin-only’ structureshows no strain. An amorphous silicon deposition added to annealinginduces a strain in the opposite direction to TiN. The amorphous siliconlayer itself induces no strain. Based on the aforementioned results, themost significant contributors are the TiN deposition and the annealingof the amorphous silicon. The purpose of removing the n-typeworkfunction metal not only provides the right threshold voltage in thep-type MOSFET region, but it also reduces the impact of an unfavorablestrain in the p-type MOSFET region. Another added benefit is to free thespace between the fins as only a single layer workfunction metal insteadof two to be deposited. This leads to a potentially large volume of theensuing W gate contact to further enhance the strain effect using W as afilm known for strain generation.

FIG. 13 is an illustration of the deposition of p-type MOSFETworkfunction metal (214) in the p-type MOSFET region. As previouslymentioned, the patterning process enables individual tuning of a strainlevel and a type of strain in both n-type and p-type MOSFET.

FIG. 14 is an illustration of the deposition of W gate contact (218) inboth, the n-type and the p-type MOSFET regions. As previously mentioned,W is a film known for generating a strain, but the presence of multiplelayers, e.g., such as a high-k dielectric, interfacial layer, andworkfunction metal layer(s) underneath sandwiched between the W film andthe silicon channel leads to a poor stress coupling from the W gatecontact to the channel. Having the aforementioned patterning processfrees the space in the p-type MOSFET region, which can create a largevolume of W deposited and which potentially can lead to a better stresscoupling, is believed to improve the strain effect from the gate.Experimentally, it has been observed that with the new scheme, the holemobility and the short channel resistance reduction leads to an overallmobility enhancement because of the Tungsten applying a compressivestrain and the workfunction displaying a tensile strain. By removing thefirst layer of workfunction metal in the p-type MOSFET region, thecompressive strain can be applied to the channel in both the in-plane(220) and the off-plane (002) direction that is favorable for a holetransport. There is also a highly stress W film available if a furtherboost is required for an improved performance. The stress level measuredin the blanket films can be enhanced from 2.3 GPa to 3.5 GPa, while in acontact array, the improvement ranges from 1.6 GPa to 2.2 GPa.

FIG. 15 shows a cross-sectional view of multiple layers of the gatestack in both the n-type and p-type MOSFET regions. The n-FET firstpatterning freezes up the space for the W fill to induce the channelstrain from the gate, where the p-type FET consists of only a very thinTiN metal that leaves sufficient room for the W fill along the PC andthe fin direction. Experimental data suggests the proposed devicestructure improves long-channel and short-channel mobility significantlyin an advanced CMOS technology. The high stress W film can also beincorporated to further boost the performance.

While the present invention has been particularly described, inconjunction with a specific preferred embodiment, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

What is claimed is:
 1. A method of forming a semiconductor devicestructure comprising: forming fins on a substrate; forming a gate stackover said fins, leaving a source region and a drain region exposed;forming a thin layer of polycrystalline silicon over said fins;epitaxially growing a high GE percentage silicon germnium film on top ofsaid polycrystalline silicon; and forming a transistor channel bywrapping said gate stack around said fins.
 2. The method as recited inclaim 1, further comprising: patterning a workfunction metal formingsequentially an n-type and p-type transistor, and depositing a stressTungsten (W) film in a space freed by patterning between said fins. 3.The method as recited in claim 1, further comprising depositing a high-kdielectric material in said gate stack.
 4. The method of claim 3,wherein said high-k dielectric material is made of HfO₂, Al₂O₃, orLa₂O₃, and said deposition is followed by performing a post depositionanneal.
 5. The method of claim 1 wherein said workfunction metalprovides a threshold voltage of said transistor producing a drivecurrent for switching a circuit.
 6. The method of claim 1 furthercomprising: depositing a thin layer of polycrystalline silicon;depositing a stress film made of high Ge percentage silicon germaniumfilm or a highly stress Tungsten film on top of said polycrystallinesilicon layer; freeing a space between said fins to position said stressfilms deposited closer to said transistor channel to improve a proximityof said stress containing material to said transistor channel; andenhancing a stress coupling efficiency by way of a ratio between astress level in said stress film, and said stress transferred to saidtransistor channel for mobility enhancement.
 7. The method of claim 6wherein said stress is enhanced by patterning to remove an n-typeworkfunction metal from a p-type transistor.
 8. The method of claim 7,further comprising stripping off a soft or a hard mask of said depositedp-type workfunction metal.
 9. The method of claim 7 wherein freeing saidspace for said p-type transistor between said fins achieves a higherstressor and better coupling from said stressor to said channel.
 10. Themethod of claim 1, wherein growing said high Ge percentage silicongermanium film on top of said polycrystalline silicon is doped in-situor ex-situ, said dopant lowering a gate resistance.
 11. The method ofclaim 10, wherein said in-situ doped film is achieved by incorporatingsaid dopants during said silicon germanium epitaxial growth, and whereinsaid ex-situ doped film is achieved by an ion-implantation followed bysaid epitaxial growing of said silicon germanium film.
 12. The method ofclaim 1, wherein a stress coupling efficiency is determined by a ratiobetween a stress level in said stressor film and a stress transferred tosaid channel for mobility enhancement.
 13. The method of claim 8 furthercomprising stripping a mask of said p-type workfunction metal depositedin both n-type and p-type MOSFET regions, and wherein freeing said spacefor said p-type transistor between said fins provides a higher stressorcoupling, and boosts a carrier mobility.
 14. A FinFET device structurecomprising: a substrate provided with fins; a gate stack on top of saidfins and an exposed source region and an exposed drain region; a thinlayer of polycrystalline silicon on top of said fins; a high Gepercentage silicon germanium film on top of said polycrystallinesilicon; and a transistor channel with said gate stack wrapped aroundsaid fins.
 15. The FinFet device structure of claim 13 furthercomprising: a high-k dielectric material on a patterned fin structurewith a recess shallow trench isolation (STI); and a workfunction metaland a thin layer of a high percentage Ge polycrystalline silicon on topof said high-k dielectric material.
 16. The FinFet device structure ofclaim 13, wherein a space between said fins and stressor films are in aproximity to said channel.
 17. The FinFet device structure of claim 14further comprising a stripped mask of said p-type workfunction metal inboth n-type and p-type transistor regions, wherein a freed space forsaid p-type transistor between said fins provides a higher stressorcoupling, for boosting carrier mobility.